update readme

README.md

@@ -4,6 +4,19 @@
 
 Sub-GHZ SPI device radio driver for STM32WL-series microcontrollers, currently supporting LoRa and BPSK.
 
+## Usage
+
+Add the dependency with `default-features = false` and enable your chip's feature:
+
+```toml
+[dependencies]
+stm32wl-subghz = { version = "0.1.0", default-features = false, features = ["stm32wle5jc"] }
+```
+
+A chip feature **must** be enabled. See `Cargo.toml` for the full list of supported chips (all STM32WLE single-core and STM32WL5x dual-core variants).
+
+> The default feature enables `stm32wle5jc` for development convenience. Always use `default-features = false` in your project to avoid feature conflicts.
+
 ## Crates
 - [`stm32wl-subghz`](.) - the driver library
 - [`examples/stm32wle5jc`](./examples/stm32wle5jc/) - usage examples for the STM32WLE5JC-based boards